Gas turbine engine annular combustion chambers comprise an inner annular wall structure, an outer annular wall structure and an annular upstream end wall structure. The annular upstream end wall structure comprises an annular head and a plurality of heat shields. The heat shields are positioned downstream of the annular head and are secured to the annular head. The inner annular wall structure comprises an annular wall and a plurality of rows of tiles and the tiles are positioned radially outwardly of the annular wall and are secured to the annular wall. The outer annular wall structure comprises an annular wall and a plurality of rows of tiles and the tiles are positioned radially inwardly of the annular wall and are secured to the annular wall.
The heat shields are provided with pedestals on their upstream surfaces and/or have effusion cooling apertures extending there-through to provide further cooling of the heat shields. The tiles on the inner annular wall structure are provided with pedestals on their radially inner surfaces and the downstream ends of the tiles in one row of tiles overlaps the upstream ends of the tiles in an adjacent row of tiles. Coolant is supplied through the annular wall to the space between the annular wall and the tiles so that the pedestals are cooled by the coolant and coolant is discharged from the downstream ends of one row of tiles to form a film of coolant on the radially outer surfaces of the tiles for further cooling of the tiles in the adjacent row of tiles. The tiles on the outer annular wall structure are provided with pedestals on their radially outer surfaces and the downstream ends of the tiles in one row of tiles overlaps the upstream ends of the tiles in an adjacent row of tiles. Coolant is supplied through the annular wall to the space between the annular wall and the tiles so that the pedestals are cooled by the coolant and coolant is discharged from the downstream ends of one row of tiles to form a film of coolant on the radially outer surfaces of the tiles for further cooling of the tiles in the adjacent row of tiles. The heat shield and tiles may also be provided with a thermal barrier coating on their surfaces facing and exposed to the hot combustion gases.
These tiles have been used extensively on rich burn combustion chambers and are able to withstand temperatures of over 2600K. This type of tiles relies on the combination of heat removal from the cold side of the tile, via the pedestals, hot side protection by the film of coolant and the thermal barrier coating.
Lean burn combustion chambers are being developed to reduce emissions of nitrous oxides (NOx). Lean burn combustion chambers operate at temperatures much less than 2600K and typically operate at a temperature of about 2300K. It might be expected that the use of the above type of tile would be obvious for a wall of a lean burn combustion chamber.
However, as mentioned previously the above mentioned type of tile has a film of coolant on the hot side of the tile. The film of coolant is actually the coolant that has flowed over, passed between the pedestals on, the cold side of the tile. The coolant used to cool the tiles is air supplied from one or more of the compressors of the gas turbine engine. Unfortunately, the presence of the film of coolant, film of air, on the hot side of the tiles may quench the combustion reactions in a lean burn combustion chamber. This is particularly important at cruise conditions, of a gas turbine engine, when the flame temperature in the lean burn combustion chamber may be as low as 1800K. This quenching of the combustion reactions may result in combustion inefficiency and increased fuel burn for the gas turbine engine.
The situation may be remedied by modifying the combustion process, such as by scheduling extra fuel to the pilot combustion zone of the lean burn combustion chamber, by supplying more fuel to the pilot injector of the fuel injector, so that the pilot zone operates at a higher temperature and helps to consume any inefficiency in the main combustion zone of the lean burn combustion chamber. Unfortunately, the rescheduling of extra fuel to the pilot combustion zone of the lean burn combustion chamber, during cruise conditions of the gas turbine engine, also increases the emissions of nitrous oxides (NOx).
Therefore the present disclosure seeks to provide a novel combustion chamber which reduces or overcomes the above mentioned problem.